Cryogenic freezer

ABSTRACT

A rectangular double walled cryogenic freezer has a vacuum space filled with alternating layers of flexible insulating material and a reflective material. A support structure is also positioned in the vacuum space. The support structure is open-celled and provides structural support for the freezer walls to prevent wall deformation when a vacuum is drawn. The support structure may be open-cell rigid foam or a support grid sandwiched between two layers of rigid insulation material.

BACKGROUND OF THE INVENTION

[0001] This invention relates to cryogenic freezers, and, moreparticularly, to a vacuum insulated cryogenic freezer that providesincreased storage capacity and improved insulation performance.

[0002] Cryogenic freezers have a wide variety of industrialapplications, including but not limited to, storing biological materialssuch as blood, bone marrow, and micro-organic cultures. These biologicalmaterials must be maintained at low temperatures in order to be storedfor an extended period without deteriorating.

[0003] Cryogenic freezers typically are double walled, vacuum insulatedcontainers partially filled with a cryogenic liquid such as liquidnitrogen for establishing an extremely cold storage environment. Liquidnitrogen has a low boiling point of 77.4 K (−320.4° F.). Since cryogenicliquids have a low boiling point and, thus, a low heat of vaporization,heat inflow from the ambient can cause significant losses of cryogen dueto the evaporation.

[0004] In order to minimize the amount of cryogen lost due toevaporation, the cryogenic freezer requires thermal and radiant barrierssuch as insulation and a high vacuum between the container walls. Thevacuum space can also be filled with multiple layers of insulation toreduce heat transfer.

[0005] An example of multi-layered insulation is a low conductive sheetmaterial comprised of fibers for reducing heat transfer by conduction.Also, the insulation can comprise radiation layers that are combinedwith the fiber layers. The radiation layer reduces the transmission ofradiant heat in the freezer see, for example, U.S. Pat. No. 5,542,255 toPreston et al. and U.S. Pat. No. 5,404,918 to Gustafson.

[0006] The insulation and vacuum chambers of prior cryogenic freezersaddress the heat transfer problems due to the low boiling point of thecryogen. But, the characteristics of the insulation materials poselimitations to the physical design of the cryogenic freezers.

[0007] Containers have been designed with the vacuum space capable ofmaintaining a low pressure of 0.1 microns when the container is holdinga cryogen. Such containers, however, typically feature a round, oval, orcylindrical shape. Such shapes provide the structural strength requiredby the walls of the container when such a high vacuum is drawn. If thesecryogenic freezers were rectangular, the walls would collapse or deformwhen the vacuum is drawn due to insufficient structural support.Typically, the insulation materials disposed in the vacuum space of flatpanel freezers fail to provide enough structural support for thecontainer walls. Thus, the shape of the container is limited tocylindrical shapes.

[0008] Accordingly, it is desirable to provide a cryogenic freezer withoptimum storage capacity such as a cube or rectangular enclosure whichenables the walls of the freezer to maintain their shape when a highvacuum is drawn.

[0009] A rectangular cryogenic freezer that addresses the above issuesis disclosed in U.S. Pat. No. 6,230,500 to Mao et al. The Mao et al.'500 patent discloses a rectangular freezer with a vacuum space that isfilled with alternating layers of reflective material and threedimensional geometric grid support structure material. The reflectivematerial is comprised of pieces of reflective foil surrounding aninsulating material, such as SUPERGEL foam, manufactured by the CabotCorporation of Boston, Mass. While effective, a disadvantage of thefreezer of the Mao et al. '500 patent is the added costs andmanufacturing complexity of using multiple support structure layers. Inaddition, the three dimensional geometric grid material and reflectivematerial of the Mao et al. '500 are expensive to construct.

[0010] Accordingly, it is an object of the present invention to providea cryogenic freezer that offers maximum storage capability at a low costwith flat interior and exterior walls.

[0011] It is another object of the present invention to provide acryogenic freezer with reduced thermal conductivity and radiant energytransfer.

[0012] It is another object of the present invention to provide acryogenic freezer that is economical to construct.

SUMMARY OF THE INVENTION

[0013] The present invention is a cryogenic freezer for storingmaterials at temperatures deviating greatly from ambient. The freezerincludes inner and outer containers, each having four walls and abottom. The inner container is positioned within the outer container andthe tops of their walls are sealed so that a vacuum space is definedtherebetween. A plurality of alternating layers of reflective materialand a flexible insulating material are positioned in the vacuum spaceadjacent the walls of the inner container. A support structure ispositioned in the sealed vacuum space with one side positioned adjacentto the plurality of alternating layers and the other side adjacent tothe walls of the outer container. The support structure substantiallyreduces deflection of the walls when air is evacuated from the vacuumspace.

[0014] The support structure may be a support grid sandwiched betweentwo layers of rigid insulating material. The support grid includes afirst set of parallel strip members oriented perpendicular to a secondset of parallel strip members so that a plurality of cells are formed.Openings are provided in the parallel strip members so that the cellsare open. Alternatively, the support structure may be an open-cell foammaterial. The vacuum space also includes a molecular sieve for absorbinggases therein. A sealable vacuum port is formed in the outer containerand is in communication with the vacuum space so that a vacuum may bepulled on the vacuum space.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side elevation view showing a section of a firstembodiment of the cryogenic freezer of the present invention;

[0016]FIG. 2 is an enlarged sectional view taken along line 2-2 of FIG.2 showing the support grid and the reflective material that are insertedbetween the inner and outer container;

[0017]FIG. 3 is a perspective view of the support grid of the cryogenicfreezer of FIGS. 1 and 2;

[0018]FIG. 4 is a top view of the support grid of FIG. 3;

[0019]FIG. 5 is a side elevation view showing a section of a secondembodiment of the cryogenic freezer of the present invention;

[0020]FIG. 6 is an enlarged sectional view taken along line 6-6 of FIG.5 showing the support foam and the reflective material that are insertedbetween the inner and outer container.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] With reference to FIG. 1, a first embodiment of the cryogenicfreezer of the present invention is indicated generally at 10. Thecryogenic freezer 10 features an inner container 12, an outer container14, and a vacuum space 16 therebetween. The inner container 12 and outercontainer 14 are preferably constructed from stainless steel. Typicalfreezer dimensions are 27″×27″×35″ (L×W×H).

[0022] The freezer 10 is cubic or box-shaped and the inner container 12and the outer container 14 each have four square or rectangular sidewalls and a square or rectangular bottom. A top 15 is pivotallyconnected to the top edge of the freezer. The rectangular freezer takesup the same amount of floor space as cylindrical shaped cryogenicfreezers commonly known in the art. The larger volume of the rectangulardesign, however, provides additional storage space in the freezer.

[0023] As illustrated in FIG. 2, the vacuum space 16 containsalternating layers of a reflective material 18 and a flexible insulatingmaterial 20 adjacent to inner container 12. A support structure in theform of a support grid 22 sandwiched between two layers of rigidinsulation material 26 a and 26 b is positioned between the outercontainer 14 and the alternating reflective and flexible insulatingmaterial layers.

[0024] As illustrated in FIG. 1, the vacuum space includes a molecularsieve 24. The molecular sieve 24 can be, but is not limited to, a carbonor ceramic based material. The molecular sieve 24 is preferably laid onthe outside bottom surface of the inner container 12 during assembly.The molecular sieve 24 addresses the problem of out-gassing andchemically absorbs gas remaining after a vacuum is drawn.

[0025] Alternatively, getters, commonly known in the art, can be placedat the bottom of the freezer in the vacuum space. The getters alsoaddress the problem of out-gassing. The getters chemically absorb thegas remaining after a vacuum is drawn.

[0026] Turning to FIG. 2, the reflective material 18 is preferablycomprised of sheets of reflective foil. An example of a suitableflexible insulating material 20 is insulation paper such as CRYOTHERM243 insulating paper from the Lydall Corporation of Manchester, Conn. Atleast one layer of the flexible insulating material 20 is placed oneither side of the reflective foil 18. The air between the reflectiveand flexible insulating material layers is evacuated as the vacuum space16 is evacuated. The reflective foil reduces the radiant energy that istransmitted through the vacuum space 16 between the inner container 12and the outer container 14. The flexible insulating material 20 providesa thermal barrier between each layer of reflective foil.

[0027]FIG. 3 illustrates, in general at 22, a perspective view of thesupport grid. The support grid 22 features a first set of parallel stripmembers 23 that are oriented in perpendicular fashion to a second set ofparallel strip members 24. As a result, as illustrated in FIG. 4, anumber of cells 25 are formed. As illustrated in FIGS. 1, 2 and 3, theportions of the strip members 23 and 24 defining the walls of each cell25 are provided with openings 27. As a result, the support grid 22features an open-cell configuration to allow air to be evacuated out ofthe vacuum space 16 to form the vacuum. The open-cell grid structurealso enables the molecular sieve 24 to absorb residual moisture and gasin the vacuum space to insure long vacuum life.

[0028] The support grid preferably is constructed from a composite,plastic, or ceramic material. The support grid 22 material should beselected to limit the thermal conductivity and control out-gassing inthe vacuum space. A list of appropriate materials for the support grid22 includes, but is not limited to, T304 stainlesss steel, polyurethane,Ryton R4, Vectra LCP, Vectra E130, Noryl GFN-3-801, Ultem 2300, Valox420, Profax PP701N, polypropylene and Nylon 66.

[0029] The support grid 22 provides physical support to the walls of theinner and outer containers 12 and 14 of the cryogenic freezer so thatwhen a vacuum is drawn in vacuum space 16, they do not collapse. Thesupport grid 22 can withstand the maximum pressure at full vacuumbecause of its grid structure. The support grid 22 uniformly distributesthe load on the walls of the inner and outer containers 12 and 14. Thus,the thickness of the walls of the inner and outer containers 12 and 14,respectively, can be reduced.

[0030] The low heat transfer coefficient of the support grid 22minimizes the heat conducted from the outer container 14 to the innercontainer 12. The support grid 22 also reduces heat conductivity bymaximizing the open space and minimizing direct contact between thesupport grid 22 and the layers of rigid insulation material 26 a and 26b (FIG. 2).

[0031] As stated above and illustrated in FIG. 2, the support grid 22 issandwiched between two layers of rigid insulation material 26 a and 26b. The rigid insulation material preferably is G-11 fiberglass sheeting.The rigid insulation material provides additional thermal insulationbetween the support grid 22 and the outer container 14 as well asbetween the support grid and the alternating layers of reflectivematerial 18 and flexible insulation material 20. In addition, rigidinsulation material 26 a prevents the edges of support grid 22 fromtearing the reflective and flexible insulation materials 18 and 20.

[0032] The cryogenic freezer 10 is assembled by placing the molecularsieve 24 on the outside bottom surface of the inner container 12.Alternating layers of the reflective material 18 and flexible insulation20 are layered in the vacuum space such that the first and last layerplaced are flexible insulation 20. The number of layers is preferablythirty or less. This is followed by the rigid insulation material 26 a,then the support grid 22 and then the rigid insulation material 26 bwhich abuts the inside surface of the outer container 14. After theinner container 12 is positioned within the outer container 14, theannular opening between the two at the top of the freezer is closed witha ring-shaped top plate, illustrated at 30 in FIG. 1. The top plate 30is welded to the top edges of the inner container 12 and the outercontainer 14 to seal the space between them, that is, vacuum space 16.

[0033] A vacuum is drawn in space 16 to increase the insulation value ofthe freezer. The cryogenic freezer 10 includes a port 28 (FIG. 1) in theouter container 14 for that purpose. The port 28 may be located at therim of the top or on the bottom of the freezer. (A vacuum pump isconnected to the port 28 to evacuate the air in the vacuum space 16.Thereafter the port is sealed.

[0034] A second embodiment of the cryogenic freezer of the presentinvention is indicated in general at 110 in FIG. 5. As with theembodiment of FIGS. 1-4, the freezer includes an inner container 112 andan outer container 114 with a vacuum space 116 therebetween. The innerand outer containers each include four rectangular or square side wallsand a square or rectangular bottom so that the freezer is cubic orbox-shaped. In addition, as with the embodiment of FIGS. 1-4, amolecular sieve 124 or a getter is positioned within the vacuum space116 to absorb gas therein. A top 115 is pivotally connected to the topedge of the freezer.

[0035] As illustrated in FIG. 6, the vacuum space 116 is filled with afoam support structure 122 and, as with the embodiment of FIGS. 1-4,alternating layers of reflective material 118 and flexible insulation120. The reflective material 118 and flexible insulation 120 may beconstructed of the same materials recited above with reference toreflective material 18 and flexible insulation 20 in FIG. 2.

[0036] The foam support structure 122 replaces the support grid andrigid insulation layers (22, 26 a and 26 b, respectively, in FIG. 2) ofthe embodiment of FIGS. 1-4. The rigid open cell foam support 122 maybe, but is not limited to, plastic, metallic or ceramic open cell foam.The foam material should be selected to limit the thermal conductivityand control out-gassing in the vacuum space. For example, the supportfoam material may be, but is not limited to, stainless steel,polyurethane or polystyrene.

[0037] The support foam provides physical support to the walls inner andouter containers 112 and 114 so that when a vacuum is drawn on vacuumspace 116, they do not collapse. The support foam 122 can withstand themaximum pressure at full vacuum because of its cellular structure. Thesupport foam 122 uniformly distributes the load on the walls of theinner and outer containers 112 and 114. As a result, the thickness ofthe walls may be reduced.

[0038] The support foam 122 is configured with an open-cell structure toallow air to be evacuated out of the vacuum space 116 to form thevacuum. The open-cell foam structure enables the molecular sieve 124 toabsorb residual moisture and gas in the vacuum space 116 to ensure longvacuum life for the freezer. As with the embodiment of FIGS. 1-4, thelow heat transfer coefficient of the support foam 122 minimizes the heatconducted from the outer container 114 to the inner container 112. Thesupport foam 122 also reduces heat conductivity by maximizing the openspace.

[0039] The cryogenic freezer 110 is assembled by placing the molecularsieve 124 on the outside surface of the bottom of the inner container112. Alternating layers of the reflective material 118 and the flexibleinsulation 120 are then placed in the vacuum space 116 such that thefirst layer placed against the inner wall 112 is flexible insulationmaterial. Preferably up to 30 layers are formed with the last sheetbeing a sheet of flexible insulation material. The support foam 122 isnext positioned so as to rest between the layers and the walls of outercontainer 114 when the freezer is assembled. Once the inner container112 is properly positioned within the outer container 114, the resultingopen annular top is closed, and the vacuum space 116 sealed, by aring-shaped top plate 130 that is welded to the top edges of the wallsof inner container 112 and outer container 114 (FIG. 5).

[0040] As with the embodiment of FIGS. 1-4, a vacuum is drawn in space16 to increase the insulation value of the freezer. The cryogenicfreezer 110 includes a sealable port 128 (FIG. 5) in the outer container114 that connects to a vacuum pump for that purpose.

[0041] While the preferred embodiments of the invention have been shownand described, it will be apparent to those skilled in the art thatchanges and modifications may be made therein without departing from thespirit of the invention, the scope of which is defined by the appendedclaims.

What is claimed is:
 1. A cryogenic freezer for storing materials attemperatures deviating greatly from ambient comprising: a) an innercontainer, said inner container comprising four walls and a bottom; b)an outer container enclosing the inner container and defining a vacuumspace therebetween, said outer container comprising four walls and abottom, said inner container being connected to the outer container atthe top of said walls to seal said vacuum space; c) a pluralityalternating layers of reflective material and flexible insulatingmaterial; and d) a support structure positioned in the sealed vacuumspace with one side positioned adjacent to the plurality of alternatinglayers, said support structure substantially reducing deflection of thewalls when air is evacuated from the vacuum space.
 2. The cryogenicfreezer of claim 1 wherein said support structure is a support grid. 3.The cryogenic freezer of claim 2 wherein the support grid includes afirst set of parallel strip members oriented perpendicular to a secondset of parallel strip members so that a plurality of cells are formed.4. The cryogenic freezer of claim 3 wherein openings are provided insaid parallel strip members so that the cells are open.
 5. The cryogenicfreezer of claim 4 where the support grid is sandwiched between layersof rigid insulation material.
 6. The cryogenic freezer of claim 2wherein the support grid is sandwiched between layers of rigidinsulation material.
 7. The cryogenic freezer of claim 6 wherein therigid insulation material is fiberglass sheeting.
 8. The cryogenicfreezer of claim 1 where in the support structure is open-cell foam. 9.The cryogenic freezer of claim 1 wherein the vacuum space also includesa molecular sieve for absorbing gases therein.
 10. The cryogenic freezerof claim 1 wherein the flexible insulation material is insulation paper.11. The cryogenic freezer of claim 1 wherein the reflective material isreflective foil.
 12. The cryogenic freezer of claim 1 further comprisinga sealable vacuum port formed in the outer container.
 13. The cryogenicfreezer of claim 1 wherein the plurality of alternating layers areadjacent to the inner container and the support structure is adjacent tothe outer container.
 14. A method for assembling a doubled walled vacuuminsulated cryogenic freezer for storing materials at temperaturesdeviating greatly from ambient comprising the steps of: a) providing aninner container with four walls and a bottom; b) positioning a pluralityof alternating layers of reflective material and flexible insulatingmaterial adjacent to the inner container; c) positioning a supportstructure adjacent to the plurality of alternating layers for preventingdeflection of the walls and bottom surface when a vacuum is drawn; d)positioning the inner container in an outer container, the outercontainer having four walls and a bottom, to define a vacuum spacetherebetween; e) connecting the inner container to the outer containerat the top walls to seal the vacuum space; and f) evacuating air fromthe vacuum space.
 15. The method of claim 14 further comprising the stepof sandwiching the support structure between two layers of rigidinsulation material.
 16. The method of claim 15 wherein the rigidinsulation material is fiberglass sheets.
 17. The method of claim 14wherein the flexible insulation material is insulation paper.
 18. Themethod of claim 14 wherein the reflective material is reflective foil.19. The method of claim 14 wherein the support structure is a supportgrid.
 20. The method of claim 14 wherein the support structure isopen-cell foam.